1. Field of the Invention
This invention relates to the manufacture of delayed petroleum coke, and more particularly to an improved method of quenching a drum of coke. The method is applicable to a delayed coking process wherein a coke feedstock is heated in a furnace to coking temperature, introduced into a coking drum, and maintained therein at coking conditions until delayed petroleum coke is formed. After completion of the coking reaction, it is conventional to inject steam into the coking drum to vaporize volatile hydrocarbons remaining in the drum. These volatile hydrocarbons normally are passed to a fractionator for recovery or recycle. Following removal of volatile hydrocarbons from the coke in the coking drum, injection of steam is normally continued, with discharge of same to a blowdown tank. Following completion of the steaming step, it is conventional to inject quench water into the lower part of the coking chamber, whereby the delayed coke is cooled to below ignition temperature prior to removal of the coke from the coking drum. The quench water is converted to steam as it passes through the coke in the coking drum, and the steam tends to carry over an appreciable amount of fines into the blowdown tank to which it is discharged. This carry-over of fines to the blowdown tank leads to operating difficulties and in some cases contributes to environmental problems. There has been a long standing need for a coking process which does not result in fines carry-over to the blowdown tank.
2. Description of the Prior Art
The delayed coking process has been widely utilized for many years as a method of recovering a useful product from heavy residual oils and other similar streams from a refinery process. The production of regular coke, useful primarily as a fuel, is described in many literature and patent references, of which U.S. Pat. No. 2,316,931 is exemplary. As described therein, coking feedstock is passed through a furnace and introduced into a coking chamber where delayed coke is formed. After the coking chamber is filled with coke, steam is introduced into the bottom of the coking chamber to remove volatile hydrocarbons therefrom followed by a pressure reduction or blowdown step wherein further light material is removed from the coking chamber. After completion of the steaming step, water is introduced into the bottom of the coking drum to effect cooling of the coke to below its ignition temperature so that the coke drum may be opened to the atmosphere for removal of the coke. Prior to this invention, the industry has universally followed the practice of introducing quench water into the bottom of the coking drum, with the resultant problems referred to above regarding carry-over of fines to a sump or blowdown tank.